DE2503850A1 - WAVE CONDUCTOR ANTENNA WITH APERTURE SWITCH - Google Patents

Description

Patent attorney

Dipl.-Phys. Leo Thul

7 Stuttgart 30 2503850

Short street 8 fcv.vv.vy.v

G.F. Craven-29

INTERNATIONAL STANDARD ELECTRIC CORPORATION, NEW YORK

Waveguide antenna with aperture switch.

The invention relates to one consisting of several individual radiators Transmitting or receiving antenna, in which the individual radiators are switched on one after the other and the unused ' Individual radiators are switched ineffective with regard to the radio field.

Such antennas are required, e.g. for Doppler landing ^ systems as described in DT-PS 1 249 361 or for landing systems in accordance with DT-AS 2 230 630, which with so-called virtual diagrams work.

Kg / lap
January 16, 1975

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With these antennas, the individual elements of which are used one after the other, it must be ensured that they are not switched on elements not with the switched on ' Element are coupled so that there are no undesired secondary radiation arises. This problem occurs particularly with the antennas whose individual radiators are closely spaced e.g. at a distance of less than the wavelength λ. Attempts to decouple neighboring Ensuring emitters through measures that affect the feed were not satisfactory. Especially with antennas whose individual radiators are waveguides, the decoupling was not sufficient, especially not broadband genoa.

It is therefore the object of the invention to provide a circuit arrangement for waveguide antennas that does not connect them Waveguide emitter controls ineffective and which is suitable for high switching speeds.

The task is with the anqeaebenen in the claims Funds resolved.

Since PIN diodes are used as switching elements, be now first discussed their properties.

The advent of the PIN diodes roughly in the last decade has shown an important new possibility at To be able to switch microwave frequencies quickly and with little loss.

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So the high frequency impedance of a diode can be reduced by a Range in excess of 10 000: 1 (10 000 Ω - 0.5 Ω) can be switched by removing a reverse voltage from one or two volts to a forward bias voltage passes with a flow current of 0.1 A.

This characteristic is already advantageous for micro-V7elles on coaxial lines and "microstrip lines" where it is because of the relatively small size Transverse dimensions of these line systems is possible to use the actual terminal impedance x '/ erte of the PIN diodes. In waveguides, the problem is fundamentally much more difficult and requires a different treatment.

This is shown in the following part of the description in which the invention is explained in more detail with reference to the figures, for example.

Show it:

1 shows a waveguide with a PIN diode; . -

2 shows a conductive PIN diode in a waveguide;

FIG. 3 the equivalent circuit diagram for FIG. 2;

4 shows a non-conductive PIN diode in a waveguide;

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FIG. 5 shows the equivalent circuit diagram for FIG. 4;

Fig. 6 a waveguide antenna radiator, the underneath its cut-off frequency is operated and has an aperture switch.

7 shows a waveguide with an obstacle and a additional capacity;

Fig. 8 in the Smith diagram the admittance of a radiating Element with the arrangement according to Figure 7 in the aperture;

9 shows a waveguide switch with two diodes;

Fig. 10 and Fig. 11

the equivalent circuit diagram of the switch from Fig.Q in the switched-on or switched-off state;

Fig. 12 shows the admittance of the switch in the Smith diagram according to Figure 9;

13 shows a modified form of the waveguide switch with two diodes;

14 shows the complete equivalent circuit diagram of the diode switch;

Fig. 15 and 16

the equivalent circuit diagrams derived from FIG. 14 with the switch closed and with the switch open;

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Fig. 17 and 18

the function of a transformer;

Fig. 19 a multi-stage switch in a waveguide, which is operated above its cutoff frequency;

20 shows a chain link representation of a multi-stage Switch;

Fig. 21 a multi-stage switch in a waveguide, which is operated below its Grenzfreauenz.

The basic problem when using PIN diodes in waveguides can be shown using the following example.

If a PIN diode of the type mentioned is inserted in the series branch of a transmission line, which has a characteristic impedance Z of 100 Ω, for example, its impedance in the conductive state (0.5 Ω j causes a very low transmission loss, its impedance in the non-conductive state ( 10 000 Ω), on the other hand, almost total reflection. However, if a PIN diode 1 (Fig. 1) is arranged in a waveguide 2 in the center of the waveguide by connecting it between the wide side surfaces (parallel connection is more suitable for waveguides than the Series connection) it forms an obstacle in the conductive state that comes very close to an inductive rod (3, FIG. 2). This rod corresponds in its dimensions to the connecting wires of the PIN diode connecting the opposite side surfaces and represents an inductance L _c (FIG .3).

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For a wire with a diameter of 0.5 mm and a waveguide width of 7.5 cm, a standardized reactance X / Z of Χ / Ζ τ & 1 is obtained.

When shunted with an adapted waveguide, this would result in a standing wave ratio of only about 3: 1. this must be seen against the value of 200: 1 that is found in the example of a transmission line mentioned would receive. The large discrepancy between these results is due to the well-known fact that simple resistance considerations are not valid for the calculation of the impedance of conductor arrangements in a waveguide. The normalized reactance of the obstacle under consideration is primarily by the ratio d / a (d = diameter, a = waveguide width) certainly. A larger waveguide, which is suitable for lower frequencies, results in the same diode a larger value of X / Z and consequently an even smaller standing ratio (i.e. worse switching ratio) . This phenomenon is therefore a matter of the relative dimensions and not of the operational freeness of the Waveguide.

4 shows a first approximation for the case of a non-conductive Diode. Although this is known as a capacitive rod, the representation is only correct if the rod parts do not penetrate deep into the waveguide. For greater penetration depths, the obstacle can have a series resonance

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cause and then effectively means a short circuit of the Waveguide. The equivalent circuit diagram of such an obstacle is therefore that shown in FIG. It's clear, that the impedance of this circuit can be very low, it could even be lower than that Values that can be achieved with a conductive diode. This illustrates the basic problems of diode waveguide switches and at the same time it provides an essential clue for solving the problem.

It should be emphasized that the present solution is quite general applies to waveguide switches, even if the problem of the Switching by means of a PIN diode mainly with a view to being used as an antenna waveguide switch is explained.

A single waveguide radiator of a waveguide antenna, generally considered in this specification is shown in FIG. It contains a piece of 10 of a waveguide, which is below its Grenzfrecmenz is operated, with a Koaxialeinaanct 11 and one dielectric plate 12 (capacitive loading) in the Aperture, which is located in a conductive plate 13 " finds. Such a waveguide radiator is known from DT-OS 2 328 632, for example. The switch 14 is also arranged in the aperture plane.

As already shown, the component properties of the PIN diode itself (i.e. mechanically shortest possible Length of the connecting wires) almost ideal, especially with

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low microwave frequencies. Therefore, the basic principles of the switch can be simplified using the Describe equivalent circuit diagrams (Fig. 3, Fig. 5) of the diode in the waveguide. That of these two equivalent circuit diagrams common element is the inductance L.

In "Lewin, L., Advanced Theory of Waveguides", Iliffe, 1951 "it is shown very roughly that, given the same dimensions of the HirLderniss, in both cases the value L-

Inductance is the same in both equivalent circuit diagrams, with the elements of these circuit diagrams as concentrated Elements to be considered. This will become important later when you understand it more precisely. First it becomes clear from Fig. 5, that by choosing the appropriate value of C the resonance condition for the circle formed from L · and C for each Frequency can be established. This generally requires a capacitor that is natural capacitance connected in parallel, which arises on the electric field arising in the line gap in Fig. 4. the Results that can be obtained for two values of the additional capacitance C

receives, namely for 0.5 pF and 1, OpF and with an obstacle, as shown in Fig.7, in Fig.8 shown. In the Smith diagram, this shows the curves of the input admittance value of a normal radiating one Element with this additional circuit in its aperture. For completeness is a more detailed explanation the measurement conditions are necessary, which will also be given later, but first of all the high amount of the reflection factor may be over a wide band of joy as a sign of the

COPY

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Broadband character of the short circuit apply. This result is due to the choice of a thick capacitive rod 4 (as Stepped ladder realized) as a connection for the PIN diode in the waveguide. This results in a small value of L and therefore a relatively large value of C is required to meet the resonance condition, so that the whole circle has the desired property of a small I / C ratio. .

9 shows an implementation of this circuit principle in the case of a waveguide aperture switch for a single-stage antenna element that is below its Grenzfreauenz im Frequency range from 0.962 - 1.213 GHz is operated. The switch contains two PIN diodes 1a and 1b, respectively between concentrated capacitors 15 are switched, the capacitance of which is 1.4 r> F. The usage of two diodes is of no particular importance, but has the advantage that the symmetry of the aperture is retained. The capacitors 15 are made in strip line technology Copper coating of a polytetrafluoroethylene glass fiber board manufactured. The lower Beläcre 16 of these stripline capacitors lie on the dielectric plate 12 and have direct contact with the waveguide walls. The PIN diodes 1a and 1b are between the upper conductive ones Deposits 17 of the individual strip line capacitors. The HF chokes L are used to supply the control direct current for diodes 1a and 1b.

The equivalent circuit diagrams obtained with conductive diodes and non-conductive diodes are shown in Fig. 10 and

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• Fig.11 shown. The representation of the diode in the conductive The condition as a short circuit is a certain idealization, as is the representation of the non-conductive diode as complete Interruption of the circle. However, the observation of the measured in these two conditions shows Results {Fig.12, curve A for conductive and curve B in the case of non-conductive diodes) that these assumptions were permissible. It also shows the excellent properties of PIN diodes in these applications. The admittance measurements are made at the coaxial input connection of the antenna element. This level is good creeianet for measuring the input voltage, but causes one large phase change in the admittance characteristic of the aperture switch. It's more realistic, the Bezuas level the admittance characteristic in the aperture. This requires a display of admittance values with a real short circuit (metal plate or metal strip) in the aperture. The associated measuring points are in Fig.12 - with S.C. designated. By.comparison of Points of the admittance curve in Fig. 12 with corresponding points SC of the short circuit can be used to determine the true phase shift determine. In Fig. 12 the two points coincide at 1040 HHz. This is therefore the freedom of people (L C) of the aperture switch.

The phase shift in other frances is qerina. -

Fig. 13 shows the top view of the anertur of a waveguide radiator with aperture switch. As included in Fig.9

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the aperture switch has two PIN diodes. These are located on the top of two plates 20a, 20b made of polytetrafluoroethylene glass fiber, which in turn serve as a carrier for strip conductors. Each PIN diode 1a, 1b is between the upper pads of the capacitors 15 are switched. The corresponding lower coverings are parts of the metallic ones Lower layer of the fiberglass panels 20a, 20b. right away behind it sits in a recess of the waveguide edge the dielectric plate 12. The edge of this plate 12, which can also be referred to as a capacitive diaphragm is indicated by dash-dotted lines and corresponds to the edge in Fig. 9. The fiberglass plates are with the upper and lower metallic edge 21 of the waveguide screwed. So that both the conductive connection of the lower plates of the capacitors with the waveguide walls as well as the solid Kalteruna des Diaphraomas 12 behind it reached. The undersides the fiberglass plates 20a, 20b are coated with metal only in the area shown in dashed lines. The high-frequency chokes L shown in FIG. 9 are made up of high-resistance quarter-wave lines 18 and blocking capacitors 19 replaced in stripline technology. The control inputs 22 lie on the upper plates of the blocking capacitors 19.

As in Fig.9, the connection is made so that the PIN diodes and the upper plates of the capacitors 15 connected in series are. However, these connecting lines are not shown in FIG.

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The impedance curve shown in Fig.12j curve B can be through Further methods of adaptation are made more broadly are, however, this can be done elsewhere in the antenna element and is therefore not for the invention essential.

Even if the equivalent circuit diagrams considered so far are somewhat idealized, they are good genoa, explain how the switch works. However, one can come to a more precise equivalent circuit diagram, if you look at the manufacturer's equivalent circuit diagram for. introduces the PIN diode into the complete switch, v / ie indicated by the dashed rectangle in Fig. 14 '.

Here L is the inductance of the PIN diode, R is its P '■ s

Series resistance, C your case capacitance and C_

po I

and R * their work capacity and work resistance, respectively.

This circuit can then be brought to two forms, which apply to the conductive or the non-conductive state. If you get the maximum bias current in the direction of flow (»0.1 A), the diode resistance is less than one ohm, i.e.

^V LS | '- PLP ^{+ R} s ^{+ P} 1 I.
X _T "is the reactance of a conductive rod in the hollow

leader who is so great that he has the effect of a simple The diode switch. If this is the case, the equivalent circuit diagram to which in Shape shown in Fig.15.

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With reverse voltage of the diode, R..MO 000 'Q, X _ is also relatively large, so that X _ and R can be neglected. The equivalent circuit is then reduced to that shown in FIG.

If one compares the pictures 15 and 16, which represent the diode in its two states, it is a question of series resonance circuits, one with a series and one with a shunt damping. The difference lies in the relative sizes of C and C ; C is selected in such a way that the resonance condition is fulfilled with L and the desired short circuit occurs. C is a parasitic capacitance that would ideally be zero. Hence, one of the reasons L becomes small

make it clear (wide conductor instead of a thin rod): With a small I »a large value of C is necessary, to form a given product L C. The series resonance frequency of the circuit shown in Figure 16 is oeebened by the product L C. This takes that

SD

Relationship of the series resonance frequencies of Fig. 15 and Fig. 16, which determine the effectiveness of the switch, of great value.

The function of the transformer shown in Fig.17 is on matched these properties. It is represented physically by the positioning of the diode in the Aperture. The admittance of the circle shown in Fig. 16 represents the operating frequency (non-conductive Diode) represents a capacitive susceptance value (goes infinitely with finite friency aeaen.

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This affects the bandwidth. By creeianete of the transmission ratio, this effect can affect ' Cost of less effectiveness of the short circuit ^ be reduced. The transformed admittance changes according to the expression:

"... 2 πα

γ _ γ _sxn

There

Where Y_: the admittance of the diode in each state

d: the distance from the side wall a: the waveguide width

These dimensions are shown in Fig. 18.

So the "short circuit" is most effective when the diode is in the middle of the waveguide, but the bandwidth is then the least. In the case of Fig. 9a, however, there was a large one Bandwidth necessary, and a qerina compromise on this the effectiveness of the short circuit was acceptable.

If two PIN diodes are used, the bandwidth can can be increased by slightly increasing the series resonance frequencies of the left and right circles can differ from each other.

Multi-stage PIN diode switches are known per se, and the one described here can also be used in a similar manner

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Use Schäter for this purpose. The images 19 and 21 show versions which fo _r aewöhnliche waveguide or waveguide / which are operated below their Grenzfrecmenz, are usable.

With normal waveguides, the cutoff frequency is below the operating frequency (Fig. 19), the individual stages S1, S2 and S3 are separated by a quarter wavelength. With the help of the well-known principle of impedance inversion, this network can then be used as a chain link (Fig.20), where R is the series resistance and G, the shunt conductance. The attenuation of the whole switch is then

α = nx (dB)

where η is the number of levels and χ is the attenuation of each Level is in dB.

When the switch is closed, R ■ and G are each small.

se sn

When the switch is open, P and G _{u are} both large.

se sh

Similar considerations apply to a ladder switch, in which the waveguide is operated below its cut-off frequency (Fig. 21). This contains three dielectric Capacitors 30, which generate the complex conjugate reactances required for the matching and are each provided with a diode switching stage S.

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The basic principle of the operation of a waveguide, which is operated below its cut-off frequency, is e.g. in "Waveguide Bandpass Filters Using Evanescent Modes" by G.F. Craven in Electronics Letters, Vol.2, No.7 (1966) pp.25-26 described in detail. G.F.Craven and C.K.Mok wrote in "The Design of Evanescent Mode Waveguide Bandpass Filters for a Prescribed Insertion Loss Characteristic ", I.E.E.E. MTT-19 March 1971, p.295 shown that paired Resonators of this type can be traced back to a chain link, so that the one given in FIG The illustration also applies to this example.

Although assuming the basic principle of the switch has been described by static DC biases of suitable size and polarity, then the bias voltage becomes in most practical applications quickly from one State can be switched to the other. The switch has already been used in systems in which the switching times are in the microsecond range, but also this is still far from the limit of technology. The absolute limit of the switching speed.it of the switch is the switch-off time of the diode, which is related to its possible operating frequency. With low freaks a PIN diode will rectify normally. If, therefore, a comparatively low microwave frequency is switched on is to be, the charge carrier life must be long, i.e. the rectification frequency should be relatively low. this

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results in a correspondingly low switching speed. In the present example (1 GHz) the required diode has a switch-off time of 150 nanoseconds, at 12 GHz the switch-off time of a suitable diode would be around 10 nanosecs. In general, the switch so be very quick.

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Claims (11)

G.F. Craven-29 Claims Transmitter or Fm.Ofangsantenne consisting of several individual radiators, in which the individual radiators are switched on one after the other and the unused individual radiators are switched ineffective with regard to the radio field, characterized in that the individual radiators are waveguide pieces open on one side (10, Fig. 6), that the respectively switched on Waveguide piece when operated as a transmitting antenna is fed on one side by the transmitter and radiates on the other open side or when operating as a Fmnfanasantenne receives on the open side and on the other hand the received signals to the receiver and that on the open side of the waveguide in the aperture at least one PIN diode (1a, 1b) is arranged in such a way that it switches the waveguide ineffective in its conductive state. 2. Antenna according to claim 1, characterized in that the waveguide (10) is a rectangular waveguide that each PIN diode (1a, 1b) via an RF connection, which in addition to an inductance (L) also has a capacitance (C) , is connected between opposite broad side walls, and that the HF connection forms a series resonant circuit when the PIN diode (1a, 1b) is conductive 509833/0 610 G.P. Craven-29 within the operating frequency range of the antenna. RF short circuit generated in the aperture plane. - 3. Antenna according to claim 2, characterized in that each a PIN diode (1a, 1b) containing HP connection on different sides of the PIN diode contains capacitors in stripline technology (15), the upper plates (17) of which with the PIN - Diodes (1a, 1b) and their lower plates (16) are connected to the waveguide walls so that the upper plates (17) of the capacitors (15) are connected in series via high-frequency chokes (L, 18), at the ends of which blocking capacitors (19) designed using stripline technology are connected. 4. Antenna according to claim 3, characterized in that the capacitors (15) of the HP connection, the PIN diodes (1a, 1b), the Hochfreauenzdrosseln (18) and the blocking capacitors (19) on the same dielectric carrier plate (20a,. 2Ob) are arranged and that the high-frequency chokes (18) are conductor pieces of high impedance with the length λ / 4. · 5. Antenna according to claim 4, characterized in that the inductance of the · HP connection is small and the capacitance is large. 6. Antenna according to Ansoruch 5, characterized in that only one PIN diode is provided and this is offset in time with respect to the longitudinal axis of the waveguide. 509833/0610 G. F. Craven-29 7. antenna according to claim 5, characterized in that only one PIN diode is provided and this is arranged in the center of the waveguide. 8. Antenna according to claim 5, characterized in that two PIN diodes (1a, 1b) are provided, which are arranged symmetrically offset from the longitudinal axis in the 'waveguide (Fig.9, Fig.13). 9. Antenna according to claim 8, characterized in that the resonance frequencies of the HF connections containing the PIN diodes are different to increase the bandwidth. 10. Antenna according to one of the preceding claims, characterized in that the waveguide is operated below its cutoff frequency (Fig.21). 11. Antenna according to one of claims 1 to 9, characterized in that the waveguide is operated above its Grenzfreauenz (Fig.19). 509833/0610 Blank page